America's largest nomadic tribe
28 November 2011 Last updated at 06:13 GMT
In America there is a hidden population of people who live on the country's roads, railways and open spaces, on their own or in groups.
There are about three million in the largest group of nomads, who roam the country in motorhomes or recreational vehicles (RVs) - and 90% of these RV-ers are over 55.
Richard Grant meets the tribes of American Nomads on BBC Four, Monday 28 November at 21:00 GMT.